Now that personal computers are used widely in general homes for the purpose of doing various operations, such as accessing the Internet, the word of “network” is becoming very familiar to general users. In addition, there have appeared various digital information-related home appliances such as digital video cassette recorders, digital video cameras, etc., so that users can construct even intra-home networks easily in their homes now, since those appliances are provided with an IEEE1394 interface respectively. On the contrary, the IEEE1394 standard, expecting on the basis of the experience from the SCSI bus that the standard will be used by those general users more and more, has realized a plug & play function for assigning an ID to a device automatically so as to construct such an intra-home network just by connecting the device to a network, as well as a hot plug function for enabling the device to be disconnected/connected from/to the network while the device is powered. The IEEE1394 standard has also enabled devices to be connected at higher freedom, for example, by any of the daisy chain method and the node branching method. Both methods can also be used together.
The plug & play AV system disclosed in JP-A-116819/1997, giving consideration to unskilled users, uses a digital interface that can detect each newly connected/disconnected AV device so as to enable various required settings to be made and the set items to be displayed automatically. Consequently, when the cable of an AV device is disconnected, a warning message is displayed so that the user can know which device is disconnected.
The above-described conventional technique, however, displays such a warning message after the cable disconnection, so it cannot prevent such an accidental case where a program the user has watched is shut down due to the disconnection of the AV device cable, thereby the device is disconnected from the network.